In general, an unsharp masking method or a high boost method is used as an edge sharpening method for improving the sharpness of a television screen image.
For example, as shown in FIG. 1, an unsharp masking method causes overshoot and undershoot to occur in an edge region by extracting high frequency components through the passing of an original signal through a High Pass Filter (HPF), and performing weighted adding on the high frequency components and the original signal that has been delayed by a predetermined period.
FIG. 2 illustrates a high boost method that generalizes the unsharp masking method. The high boost method not only makes the slope of an edge region steeper, but also causes overshoot and undershoot to occur by extracting low and high frequency components from an original signal and adding the low and high frequency components to the original signal.
The above methods increase the difference in the brightness of an edge region by forcibly generating overshoot or undershoot, rather than seeking the actual shape of a smooth edge, thereby causing a human's sense of vision to sense a greater quantity of sharpness. However, the above methods have the problem of image distortion, such as the generation of a banding pattern in an edge region, due to the overshoot or undershoot.